1. Field of the Invention
The present invention relates to a coffeemaker and more particularly to a gravity feed automatic coffeemaker having a water reservoir disposed above a filter basket, the reservoir having a valve that is controlled to open only after the water held in the reservoir has reached a predetermined temperature to provide a substantially even flow of water through the valve to the filter basket and across the coffee grounds contained therein.
2. Description of the Prior Art
Single pass automatic coffeemakers of the heat pump type are known to include a cold water reservoir separated from a heated channel by a one way check valve that allows cold water from the reservoir to enter the channel where a heat pump heats the water. As localized boiling occurs in the heated channel, heated water is pulsed out of the channel into a filter basket containing coffee grounds. At the start of the brew cycle, the water pulsed out of the heated channel is absorbed by the coffee grounds. When the coffee grounds can no longer absorb water pulsed into the filter basket, coffee formed by the interaction between the water and the coffee grounds is dripped from the filter basket into a coffee carafe. Typically, the first few ounces of water pulsed into the filter basket is in contact with the coffee grounds for as long as 15-20 seconds before a smooth flow of coffee from the filter basket is produced. This period of time is greater than necessary to brew the coffee resulting in over extraction such that the coffee produced at the beginning of the brew cycle has an undesirable bitter taste. Over extraction due to contact between the coffee grounds and water at temperatures that are too high for a period of time that is too long also occurs at the end of the brew cycle.
Another known type of single pass automatic coffeemaker is the displacement or siphon feed type in which preheated water is displaced from a hot water tank by cold water entering the tank through a displacement mechanism. It has been found that lime deposits can build up in the hot water tank of coffeemakers of this type with the lime deposits being passed out to the filter basket during the displacement process. Further, the temperature of the water entering the filter basket can vary from the desired brewing temperatures.
A further known single pass automatic coffeemaker is a gravity feed type of coffeemaker having a cold water reservoir with a bimetal valve disposed in its bottom. A secondary reservoir having a heater is positioned beneath the cold water reservoir. When the heater is turned on, the bimetal valve is heated causing the valve to distort and allow water to pass from the cold water reservoir to the secondary reservoir. Cold water initially passing over the bimetal valve into the secondary reservoir causes the valve to close to some extent while heat from the heater thereafter causes the valve to open slightly, movement of the valve continuing until an equilibrium point is reached. The water passed through to the secondary reservoir is heated therein and when a sufficient amount of water is present in the secondary reservoir, the water spills out through overflow holes into a filter basket disposed therebeneath.